Wireless electronic devices typically include transceiver circuitry, antenna circuitry, and other radio-frequency circuitry that provides wireless communications capabilities. During testing, wireless electronic devices under test (DUTs) can each exhibit different performance levels. For example, each wireless DUT can exhibit its own output power level, gain, frequency response, efficiency, linearity, dynamic range, etc. In an effort to take into account the radio-frequency cable path loss, a vector network analyzer (VNA) can be connected to each cable to determine its path loss. However, calibrating path loss using this approach requires a VNA and ignores path loss associated with the test fixtures and potential variations that may exist among the different test instruments in the different test stations. Failing to account for test fixture path loss and variations in the behavior of the different test instruments may result in inconsistent measurement data. For example, performance parameters measured using one test station may be offset with respect to the performance parameters measured using another test station.
In U.S. Pat. No. 8,903,672 B2, calibration equipment for calibrating multiple test stations in a test system is provided. Each test station includes a test unit, a test fixture and a radio-frequency (RF) cable that connects the test unit to the test fixture. A control test setup is used to calibrate uplink and downlink characteristics associated with each test station (e.g., to determine path loss associated with the RF cable and test fixture and variations associated with the test unit). The control test setup calibrates each test station at desired frequencies to generate a test station error (offset) table. The test unit of each test station is individually configured based on the test station error table so that offset is minimized among the different stations and so that the test stations may reliably measure hundreds or thousands of wireless electronic devices during product testing.
The cable loss of each test station is calibrated using a special control test set up. This special control test setup makes use of a calibration plate to be connected to the test fixture of each test station. This calibration setup, however, does not allow very accurate measurements and also slows down the calibration procedure.
There is a need, therefore, for an improved method for calibration and respective measuring devices allowing for calibration with sufficient accuracy.